Chemosensitive Response of Individual Nucleus Tractus Solitarius (NTS) Neurons from Adult Rats

The chemosensitive (CS) responses of individual NTS neurons from neonatal rats have been extensively studied, but few studies have examined the CS responses of NTS neurons from adult rats. We simultaneously measured the intracellular pH (pH _i ) and electrical responses to hypercapnic acidosis (HA) of NTS neurons from adult rats using the blind whole cell patch clamp technique and loading the neurons with the pH-sensitive dye pyranine through the patch pipette. We determined a preliminary calibration curve which yielded an initial pH _i in adult NTS neurons of 7.15 ± 0.07 (n = 105), considerably more acid than the pH _i in NTS neurons from neonates. We found that the response of NTS neurons to HA from adult rats was similar to what has been reported in neonatal rats, i.e. a maintained acidification with no pH _i recovery, a membrane depolarization, and an increase in firing rate. We measured the CS response in the absence and presence of synaptic blockade (0.2 mM Ca ²⁺ , 11.4 mM Mg ⁺ ) (SNB). SNB had no effect on the pH _i response to HA compared to that response in artificial cerebral spinal fluid (aCSF). Additionally, SNB had no effect on basal firing rate, the percentage of neurons that were activated by HA or the magnitude of the response. In conclusion, the CS response of NTS neurons in adults is similar to previously reported neonatal values and appears to be fully developed at birth.

Supported by NIH grants R01 HL566683, HL081823, F32 HL80877.